pH Sensors
Your challenging needs require innovative solutions that provide accurate & reliable pH measurement.
pH measures the acidity or alkalinity of a solution, which is determined by the concentration of hydrogen ions (H+) or hydroxyl ions (OH-) present. The most common method for inline pH measurement is potentiometric glass pH sensors. These sensors, sometimes called “pH probes”, work by producing an electrical voltage that is proportional to the hydrogen ion concentration in the fluid. Each pH sensor typically has three main components: a glass sensing electrode, a temperature element and a reference electrode.
If the hydrogen ion concentration of the fluid is:
Higher on the outside of the glass electrode than on the inside, a positive voltage occurs, indicating that the process is acidic.
Lower on the outside of the glass electrode than on the inside, a negative voltage occurs, indicating the process is basic.
The same on each side of the glass electrode, the voltage is zero, indicating the process is neutral.
The pH of the process fluid is then calculated by the transmitter using the voltage difference between the sensing electrode and the reference electrode.
Ideal for most general applications where coating is not an issue, these general purpose pH sensors feature a double junction reference that aids sensor resistance to harsh environments and helps prolong sensor life. The double junction protects the reference element of the pH sensor from poisoning ions, such as ammonia, chlorine, cyanides and sulfides.
Designed for accuracy and reliability in dirty process fluids, these anti-coating pH sensors feature a large area reference junction with a helical reference pathway that minimizes the effects of coating and plugging. They are also available with flat glass for better protection against abrasion from suspended solids in the process fluid.
Over time, the high temperature of process fluids can dramatically increase the rate at which the glass bulb of a pH sensor degrades, decreasing its responsiveness. For most pH sensors, every 10 °C (50 °F) increase in process temperature reduces pH sensor lifetime by half. Rosemount high-performance pH sensors are specifically designed for use when measuring pH at higher temperatures greater than 40 °C (104 °F) as they feature specially formulated temperature-resistant glass that provides a longer sensor life in applications with elevated temperatures.
These pH sensors also utilize a high viscosity reference electrolyte that provides protection against pressure effects greater than 100 psig.
When a process fluid contains harsh chemicals, some of these chemicals can diffuse through the reference junction of a pH sensor and into the reference chamber. There, they react with the reference electrode and alter its electrical potential, making the pH reading unstable and inaccurate.
These Rosemount anti-poisoning pH sensors feature a triple reference junction design. Each successive junction delays the diffusion of poisoning chemicals, making it more difficult for these chemicals to reach the reference electrode. The result is a more reliable and longer lasting pH measurement.
Because you have challenging needs, we also offer pH sensors for use in high-purity water applications, hygienic and sterile environments, hydrofluoric acid solutions and more.
Rosemount High Purity pH Panel
Rosemount Hx338+ Steam Sterilizable & Autoclavable pH Sensor
View All pH Sensors
Application Type | Product Name | VP | Pipe Tee | Submersible | Retraction | Sanitary Flange | Max Temp (F/C) | Max Pressure (psi/kPa) | Body Materials |
General Purpose | Rosemount™ 3900 General Purpose pH/ORP Sensor | ✔ | ✔ | ✔ | 212 / 100 | 100 / 790 | Ryton® | ||
Rosemount™ 389 General Purpose pH/ORP Sensor | ✔ | ✔ | ✔ | 185 / 85 | 100 / 790 | Tefzel® | |||
Tough Processes | Rosemount™ 396/396P/396R pH Sensors | ✔ | ✔ | ✔ | ✔ | 212 / 100 | 150 / 1135 | SST, Titanium, Polypropylene | |
Rosemount™ 398/398R pH/ORP Sensor | ✔ | ✔ | ✔ | ✔ | 212 / 100 | 250 / 1825 | Tefzel®, Titanium | ||
Rosemount™ 3300HT/3400HT/3500P High Performance pH Sensors | ✔ | ✔ | ✔ | ✔ | 311 / 155 | 400 / 2859 | Ryton®, Titanium | ||
Special Processes | Rosemount™ 372 Hydrofluoric Acid (HF) Resistant pH Sensor | ✔ | ✔ | 212 / 100 | 135 / 1035 | Ultem®, Kynar® | |||
Rosemount™ RBI pH Sensor | ✔ | ✔ | ✔ | ✔ | 248 / 120 | 150 / 1035 | Kynar®, Titanium | ||
Rosemount™ Hx338+ Steam Sterilizable & Autoclavable pH Sensor | ✔ | ✔ | 266 / 130 | 43 / 600 | Glass |
Rosemount pH sensors can help eliminate one of the biggest hassles of pH measurement – field calibration. Traditional calibration methods require taking buffers and rinse solutions from a lab to each pH sensor installation point. Rosemount pH sensors can be delivered with factory calibration embedded into the sensor’s memory, making set-up quick and easy. Simply connect the pH sensor to a Rosemount transmitter, and the latest settings can be automatically uploaded.
Data that can be stored in the pH sensor and transmitter include:
Slope
Reference Offset
Glass Impedance
Reference Impedance
Time Stamp
Sensor Serial Number
Manufactured Date
When recalibration is needed, Rosemount pH sensors can be taken to the lab for recalibration in a safe, controlled environment. pH sensors can also be calibrated in advance and stored until needed. Once reinstalled in the process location and connected to the transmitter, the pH sensor’s diagnostic history is visible to help you troubleshoot any potential issues.
pH sensors require careful monitoring to help ensure they are functioning properly and to provide an understanding of the process effects on the sensor. Many Rosemount pH sensors can provide real-time monitoring to keep you informed.
Live Diagnostics:
Glass Impedance evaluates pH sensor condition and performance which can indicate coating and exposure to high temperature.
Reference Impedance and mV Input can indicate coating, poisoning and high temperatures.
Faults & Warnings: Set points for faults and warnings can be programmed from the host or at the measurement point.
pH Slope: Reflects the pH sensitivity of the glass electrode.
mV Offset: Cumulative error of the reference cell. High offsets are indicative of coating or poisoning conditions in the process.
Rosemount pH sensors work together with Rosemount liquid analysis transmitters to provide accurate and reliable diagnostic information to help keep you informed. The transmitters are offered with a variety of options, including 2-wire, 4-wire, multiple sensor inputs and more. An explosion-proof transmitter designed to perform in harsh environments is also available.
Extend the life of your Rosemount pH sensors and transmitters, maximize your processes and reduce downtime with Lifecycle Services. From simple repairs to complex projects, Emerson supports you with services that improve the maintenance, reliability and performance of your products. Learn more.
This video demonstrates how Rosemount™ pH sensors work. pH is a measure of the concentration of hydrogen ions in a fluid, and the most common method for online pH measurement is potentiometric glass pH sensors. The sensors' two primary components -- a pH senstiive electrode and a reference electrode -- produce an electrical voltage that is proportional to the hydrogen ion concentration in the fluid. Learn more at Emerson.com/RosemountLiquidAnalysis.
This video demonstrates how Rosemount™ pH sensors function in harsh chemical applications. In these applications, pH measurement can be challenging, requiring frequent sensor replacement. Rosemount 389 pH sensors are designed with a triple reference junction to enable a longer-lasting, more reliable pH measurement.
This video demonstrates how Rosemount™ pH sensors function in harsh chemical applications. In these applications, pH measurement can be challenging, requiring frequent sensor replacement. Rosemount 389 pH sensors are designed with a triple reference junction to enable a longer-lasting, more reliable pH measurement.
The Rosemount 3900 pH Sensor / ORP Sensor features a double junction reference that aids in the sensors' resistance to harsh environments and helps prolong sensor life. The double junction protects the reference element from poisoning ions-such as ammonia, chlorine, cyanides, and sulfides. Both sensors are made with a porous Teflon® junction. The robust ph/ORP sensor design provides reliability in a wide range of aqueous solutions found in pipelines, open tanks or ponds.
The Rosemount 3400HT High-Performance pH / ORP Sensor, with integral cable, incorporates several design innovations that prolong sensor life in difficult hot processes. High temperatures, fouling, coating and poisoning conditions cause increased deterioration of the glass sensing membrane. Use the Rosemount 3400HT pH/ORP sensor to lower your total cost of ownership and reduce sensor replacement.
The Rosemount 3300HT High Performance pH Sensor / ORP Sensor, with integral cable, features a robust design that significantly prolongs sensor life in complex applications. The rebuildable pH/ORP sensor works well in high temperature and high pressure processes and resist fouling, coating and poisoning. Compared to other sensor designs, the Rosemount 3300HTVP pH/ORP Sensor decreases the frequency of sensor replacement and provides faster pH/ORP measurement response times and decreased drift.
The Rosemount 389 pH Sensor / ORP Sensor, with integral cable, is housed in a molded Tefzel™ body with Viton™ o-rings, making each sensor virtually indestructible and chemically resistant. Complete encapsulation eliminates leakage or high humidity problems traditionally found in other pH/ORP sensor designs. The simplified construction, designed with user convenience in mind, does not require electrolyte (KCl) replenishment or any high maintenance troubleshooting procedures.
The Rosemount 396P pH Sensor/ORP Sensor, with integral cable, is specifically designed for improved life in harsh, dirty, and abrasive applications such as lime slurry waste treatment, paper machine headbox and pigment/dye applications, where large quantities of suspended solids are present. The pH/ORP sensor features a coating resistant TUpH large area reference junction and a rugged polypropylene body construction for maximum chemical resistance.
The Rosemount 398 pH Sensor / ORP Sensor, with integral cable, features a chemical-resistant construction of Tefzel™ and titanium. This pH/ORP sensor is ideal for measuring pH in harsh process liquids and can be used to measure pH levels in sour water strippers, pulp bleaching towers that use chlorine dioxide, and process streams containing a variety of organic solvents.
FAQs
Sometimes called pH probes, pH sensors are used to measure the concentration of hydrogen ions in a fluid to determine the acidity or alkalinity. The pH scale ranges from 0 - 14, with a pH measurement of 7 indicating a neutral solution. Any reading below pH 7 is acidic, and any reading above pH 7 is basic.
pH sensors feature a pH-sensitive electrode and a reference electrode consisting of metal wire suspended in a stable, neutral electrolyte solution. The reference electrode maintains a steady reference voltage and completes the electrical circuit with the pH-sensitive electrode by allowing a small number of ions to flow from the reference solution into the process solution through a small porous opening called a reference junction. The pH-sensitive electrode has a small bulb at its tip that is made of pH-sensitive glass. The electrical voltage across this bulb changes in response to the hydrogen ion concentration of the process fluid around it.
If the hydrogen ion concentration is higher on the outside of the glass bulb than on the inside, a positive voltage occurs, indicating that the process is acidic. If the hydrogen ion concentration is lower on the outside of the glass than on the inside, a negative voltage occurs, indicating the process is basic. If the hydrogen ion concentration is the same on either side of the glass electrode, the voltage is zero, indicating the process is at a neutral pH of 7.
A two-point buffer calibration is the best way to ensure that a pH sensor provides accurate measurements. During a two-point calibration, the transmitter calculates new values for slope and zero offset. To calibrate, immerse the pH sensor in the first buffer solution. Allow the pH sensor to adjust to the buffer temperature (to avoid errors due to temperature differences between the buffer solution and sensor temperature) and wait for readings to stabilize. Once the transmitter has acknowledged the first buffer, rinse the buffer solution off the sensor by pouring a small amount of the second buffer solution over the tip of the sensor. Then immerse the sensor in the second buffer solution and repeat the process. Once the transmitter has acknowledged both buffer solutions, a new pH sensor slope is established.
Temperature changes within a process fluid can affect the accuracy of pH readings. The pH level of a solution is inversely proportional to the temperature. When temperature increases within a solution, the pH level will decrease, making the solution more acidic. All Rosemount pH sensors include a temperature element to adjust for any temperature fluctuations.
Yes, many pH sensors can also measure oxidation-reduction potential (ORP), sometimes referred to as redox potential. While pH sensors measure the acidity or alkalinity of a solution based on the activity of hydrogen ions, ORP sensors measure the redox potential of a solution based on the activity of oxiders and reducers in the solution.
Emerson pH sensors are used across an array of industries. For example, oil and gas industries use pH measurements for crude distillate refining, tail gas clean-up and sour water stripping. Chemical industries rely on pH measurement for the chlor-alkali process, sulfuric acid production and more. Wastewater industries use pH for desalination and water purification. For more examples and in-depth applications, please see the pH Sensor Applications below.
Most pH sensors are disposable, but some can be rebuilt and reused, such as the Rosemount 3300/3400/3500 pH Sensors. With these pH sensors, the reference electrolyte and reference junction can be replaced, and the sensor can be reused after. Some processes can coat the pH glass. In these situations, retractable probes can allow for easy cleaning and recalibration of the sensor before reinsertion.
Every application is different, each with its own unique needs and challenges. Emerson offers pH sensors that work across various industries like chemical, oil and gas, wastewater and more. If you require a pH sensor for use in high temperatures, dirty process fluids, harsh chemicals, or other unique applications, we have a pH sensor solution.
A pH sensor is connected via cable to a liquid analysis transmitter, sometimes called a liquid analyzer. The transmitter receives raw voltage signals from the pH sensor then converts the raw signals to display the pH readings.
The lifespan of a pH sensor varies based on its application. In general purpose applications like purifying water, a pH sensor can last up to two years. In high temperatures or harsh chemical applications, a pH sensor may only last for up to six months.